A toxic thyroid nodule causes hyperthyroidism (an overactive thyroid). This occurs when a single nodule (or lump) grows on the thyroid gland causing it to become enlarged and produce excess thyroid hormones. If the increased hormone production is coming from a single nodule in the gland, this is called toxic adenoma. If there are many nodules causing the hyperthyroidism, this is referred to as multinodular goitre.
The thyroid gland needs iodine to produce the thyroid hormones thyroxine and triiodothyronine. If iodine is lacking in the diet, the thyroid initially cannot produce enough thyroid hormones. Low levels of thyroid hormones cause the thyroid gland to grow as it works harder to absorb as much available iodine from the bloodstream as possible in order to make more thyroid hormones.
The UK has only borderline iodine sufficiency, and has been previously iodine deficient.
The symptoms of a toxic thyroid nodule are a result of the high levels of thyroid hormones in the blood, increasing the rate at which the body is working. Similar to those of hyperthyroidism, these symptoms include:
Signs are similar to those of hyperthyroidism (warm sweaty palms and tremors), but can also include a prominent thyroid gland with a distinct nodule.
Thyroid disorders are much more common in women than in men. Figures from the USA state that the incidence of toxic thyroid nodules accounts for 3–5% of patients with hyperthyroidism. Toxic nodules are more common in elderly people, particularly in areas of iodine deficiency.
Currently, toxic nodules are not thought to be inherited.
Diagnosis is very similar to that of hyperthyroidism. A blood test is carried out to measure thyroid hormone levels and a full medical history should be taken. The thyroid gland will be examined for presence of nodule(s). Thyroid antibodies are used to assist in diagnosis (in Graves’ disease, antibodies are typically positive as opposed to nodular disease which is antibody negative).
An ultrasound scan of the neck may be carried out to assess the thyroid nodule, and a tissue sample may be taken for analysis. This involves inserting a small thin needle into the nodule to collect a tissue sample, which can then be analysed in the laboratory. This procedure is not painful, but can feel uncomfortable.
In a small number of cases, if the swelling is large, other tests such as lung function tests may be carried out to assess whether breathing is affected. Rarely, a computerised tomography (CT) scan may also be performed to obtain a more detailed image of the gland.
A thyroid iodine uptake scan may also be performed. This is a test to measure how much iodine is taken up by the thyroid gland and gives an indication of whether the thyroid gland is under or overactive. In the case of a toxic nodule, you can see one area of increased uptake of iodine, with the rest of the gland suppressed.
All these investigations can be performed in the outpatient department.
There are three main treatment options:
A minority of patients (around 1%) experience a sore feeling or discomfort in the front of the neck following radioiodine treatment. The radioiodine can also cause the thyroid gland to become underactive in a minority of cases. The patient would then need to take tablets for life to replace the thyroid hormone.
It is also important for patients having radioiodine treatment to stay away from children and pregnant women for three weeks to avoid exposing them to radiation. Patients should speak to their doctor about pregnancy as it should be avoided for up to six months after treatment. Patients should discuss any concerns with their doctor. More information on the practicalities of radioiodine treatment can be obtained from the hospital’s Medical Physics department where the treatment will take place.
There are general risks of surgery and anaesthesia, which should be reviewed by the surgeon or anaesthetist. Further rare side-effects include damage to the recurrent laryngeal nerve, which runs close to the thyroid gland in the neck, and can affect or alter a patient’s voice if damaged (causing a hoarse voice). The parathyroid glands are attached to the thyroid and can be temporarily or permanently injured during the surgery causing hypoparathyroidism. This would require the patient to take calcium and vitamin d supplements for life. However, in some cases one of the parathyroid glands can be preserved in the body and normal parathyroid function is restored. These should be discussed with the patient before surgery.
If the whole thyroid gland is removed, thyroid hormone replacement tablets (thyroxine) will need to be taken for life.
Taking carbimazole tablets can cause side-effects such as reducing the number of white blood cells in the body; however, this is very rare. Patients who develop a sore throat or raised temperature whilst taking carbimazole should see their doctor as soon as possible.
The long-term implications of a toxic thyroid nodule or adenoma depend on the treatment option used. Patients taking carbimazole tablets will likely need to take them daily for life. Blood tests should be carried out regularly to monitor thyroid hormone levels and to adjust the dose of carbimazole accordingly. The majority of patients are able to find a medication regime that works for them and go on to live full, active lives.
If untreated, besides feeling poorly and unwell, the patient is also at risk of heart dysfunction or failure due to the increased heart rate and raised metabolic state. This irregular heart rate can result in strokes and dizziness. Long-standing toxic nodules can also affect the patient’s bones and cause osteoporosis, which results in weak bones that are more likely to fracture.
The patient may also develop symptoms due to the enlarged thyroid gland such as difficulty with breathing or swallowing (as the enlarged gland may press on the food or wind pipes, which are located nearby). If patients have any concerns about this condition, they should discuss them with their doctor.
Last reviewed: Mar 2018